A speed of the vehicle is changed by operating an accelerator and a brake, and a traveling direction of the vehicle is changed by operating a steering. However, a relation between an operating amount of those devices by the driver and an amount of change in the behavior of the vehicle is determined taking into consideration various requirements for the vehicle such as energy efficient, fuel economy, ride quality, quietness and so on.
In addition, the vehicle is driven under various environmental situations. For example, the vehicle is driven not only in an urban area but also on a highway, and sometimes vehicle climes an uphill and drives downhill. Moreover, every driver has a different preference in drive feeling, and every driver therefore receives a different impression from the vehicle in each situation. The vehicle can meet the specific driver's preference of the drive feeling under a specific environmental situation, however, if the driving situation is changed, the vehicle may not satisfy the driver's expected drive feeling. In addition, if the driver is changed, the vehicle may not provide an expected drive feeling of the different driver. In those cases, the driver may feel that he/she is required to operate the accelerator, brake, steering and so on more than necessary. For this reason, an impression about the drive feeling of the vehicle may be degraded.
In order to solve the above-explained problem, according to the prior art, the vehicle has been improved to allow the driver to select a driving mode for changing a power, acceleration, suspension etc. of the vehicle manually by a mode selecting switch. For example, according to the vehicle thus structured, the drive mode can be selected from a sporty mode where the acceleration is enhanced and hardness of the suspension is slightly hardened, a normal mode where the acceleration and suspension are moderated, an economy mode where fuel economy is improved and so on.
Various kinds of control systems for controlling behaviors of the vehicle according to a driver's preference have been developed in the prior art. According to those kinds of systems, driving characteristics of the vehicle can be customized without operating a switch. For example, Japanese Patent Laid-Open No. 06-249007 discloses a driving force control system for vehicle using a neuro-computer. Specifically, according to the teachings of Japanese Patent Laid-Open No. 06-249007, a relation between acceleration stroke and vehicle speed is learnt as a demand acceleration model, and a throttle sensibility is calculated on the basis of a deviation between the demand acceleration model and a second reference acceleration model reflecting running disposition of the driver, and a deviation between the second reference acceleration model and a standard first reference acceleration model.
Thus, the driving force control system taught by Japanese Patent Laid-Open No. 06-249007 is configured to change the driving characteristics of the vehicle in accordance with longitudinal acceleration and disposition of the driver. However, this kind of control system has to be further improved to read driver's intention.